In one recent study using retrieved joints, published in the journal Science, Dr. Jacobs and his colleagues found that a layer consisting in part of a graphic carbon – a solid lubricant with industrial applications –  forms naturally on the articulating surfaces of metal-on-metal joint prostheses in the body. While earlier research had shown that a lubricating layer forms on metallic joints as the result of friction, this was the first to discover the make-up of that layer, a discovery that could lead to ways to design better implant surface, says Dr. Jacobs. “For example, is there a way we can design alloys or design surfaces so that layer can reliably form thereby causing less debris release form wear and corrosion?”

A separate study on retrieved joints by researchers at New York’s Hospital for Special Surgery used technology called scanning electron microscopy to find new clues about the damage that occurs to failed joints. The study, which examined 46 retrieved metal-on-metal total hip prostheses from 44 patients, found that 98 percent of the cups (the portion of the implant that fits into the pelvis) and the and 93 percent of the heads (the ball at the end of the femur) showed moderate to severe scratching, while moderate to severe pitting was found in 43 percent of the cups and 67 percent of the heads. They also identified areas near the cups and head that had lost their sheen, indicating wear from friction.

“The analysis, using one of the largest collections of retrieved metal-on-metal implants, shows previously-unidentified patterns of wear,” says Douglas Padgett, MD, chief of the Adult Reconstruction and Joint Replacement Division and chief of the Hip Service at Hospital for Special Surgery.

The researchers are now using a technique called high resolution laser profiling to quantify damage in hopes of finding clues to the mechanism behind the damage, Dr. Padgett says.

Looking at patterns of wear and tear on retrieved devices not only allows scientists to better understand causes of damage, but can also enable them to develop better testing modalities for new prosthetic designs.  

“For example, to make sure that in our preclinical hip simulations – that is typically where you have a machine that mimics the motion of a hip or knee and you try to see the patterns of wear and tear – you can reproduce the patterns of wear that you see in the retrieved devices,”  says. Dr. Jacobs. “Then you have a model that you can use to test out a variety of things – new implants, new materials, adverse conditions where the implant might be functioning like malpositioning, etc.”